The present invention relates to security alarm systems and, in particular, to a telephone line seizure circuit which is attachable to each distributed telephone and or telephone jack at a monitored premises and which will seize or disconnect any "off hook" telephones. The system controller is thereby able to obtain control of the telephone line and initiate an appropriate response in the event of the necessity to report an alarm condition.
Most reporting alarm systems in use today use a switched telephone network to report alarm conditions. A requirement of such systems is that the alarm system have priority over all telephone line use during alarm reports. This need arises because of the possibility of personnel at a premises using a shared telephone line during an alarm or the possibility of picking up a premise telephone, as alarm communications are occurring and disrupting the alarm call.
The problem is corrected in most alarm systems, during system installation, by rewiring the incoming telephone line and premise telephones directly to the alarm system controller panel at the premises. Each line is connected to a line seizure relay at the panel. The telephone lines to each of the distributed telephones must therefore be routed a number of available, normally closed contacts (i.e. "swingers") at the line seizure relay.
With the activation of the line seizure relay during an alarm report, each premises telephone connected to the relay is disconnected and the telephone line is connected to the alarm communication circuitry of the system controller. The system controller then has unobstructed control over the telephone line. One or more of such relays can be provided at the system controller panel. Systems of the foregoing type are shown at U.S. Pat. Nos. 4,444,999; 4,805,210 and 4,807,278.
Another telephone line seizure scheme is shown it U.S. Pat. No. 5,465,297 and wherein an automatic telephone dialer at the alarm system controls a number of line seizure circuits distributed about the premises. Each line seizure circuit is coupled in parallel between each distributed telephone and a supporting jack. With an automatic dialer going off hook, each seizure circuit connected to the telephone line is initiated to provide a 30 second period during which parties on the off hook line can disconnect before an automatic disconnect is enabled by the automatic dialer. The automatic dialer is then able to re-connect to the freed lines and obtain control. Proper system operation requires that all telephones connected to each line include a seizure circuit.
Although the foregoing circuits free the telephone line for system access, proper installation typically requires a professional alarm system installer to make the appropriate connections. That is, a technically conversant installer must visit the premises as each telephone is added to assure proper system operation. Installer visits, however, are costly and not desired by many system owners, especially home owners with "do it yourself" alarm systems. The circuitry of the present invention was therefore developed to accommodate installation by non-technical personnel, such as the average homeowner, and yet assure proper system operation. Proper operation is assured by merely inserting a seizure circuit or "blocker", which is constructed in modular form, in series between the wall jack and each telephone, modem or other communications device coupled to the telephone line and not directly connected lo the system controller panel of the alarm system. The seizure circuits can be mounted to the front or back of each jack.
The system controller panel of the invention, in turn, includes telephone line status detection and signaling circuitry which controls the line seizure circuits to open and disable any off hook devices connected to the telephone line and permit the controller to effect an alarm report.